Process of separating toluene



g [STAT- Patented Oct. 29, 1946 rnocnss :OVFFSIEPARATINQ TOLUENEI FThomasi BiKimball, Hammond, Incl, assignor to SinclairRefinin'g Company, New York, N. Y., a

corporation of Maine I v 1 "Application-May 1 4,1941 ,,SerialNo.393,338 H 3 Cl'aims. (o1. goof-#674) This invention relates to improvementsin the the toluene from the high boiling parafim hydrocarbons, i. e., the kerosene or thelike, a relatively simple distillation operation in view of the substantial difiererice in boiling points. Substantially allof the toluene may thus be recoverediin quite pure form, e. g., 98 or better.

' Thesecond prO-du'ct'the kerosene or wash oil reifiinate, is subjected to distillation to remove the sulfur dioxide it contains, which is recycled, and then is fractionated to separate the kerosene or other high boiling hydrocarbon from the low boiling parafiin hydrocarbons and toluene which tures of toluene and paraffin hydrocarbonswhich may contain around 30- -,50% of toluene. Further concentration by distillation operations is impractical, and for this reas0n,'further concentration of the toluene is accomplished by selective extraction with sulfur dioxide, which preferentially dissolves the toluene. In such" operations, however, difliculties are encountered because of the distribution ratios between the extract and the raflinate layers.

The present invention is directed to improvements in the sulfur dioxide extraction of toluenecontaining naphtha to separate the toluene from the parafiin hydrocarbons,

'In accordance with the present invention, a mixture of toluene with parafiin'hydrocarbonsof similar boiling point is subjected to extraction, usually countercurrenhwith sulfur dioxide, and after separation of the extract from the raf- 'finate,, the extract, with or without the addition of more sulfur dioxide, iswashed or counter-currently extracted with a kerosene OIOthBI' paraffin hydrocarbon oil of substantially higher boiling T point than toluene! This jwashin'g or lcollntercurrent extraction of. the' naphthabxtract with kerosene or other relatively'high boiling,

,parafiin hydrocarbon, causes the replacement, to

a substantial extent, of the light paraflin hydrocarbons carried by the extract with heavier par aflin hydrocarbons, and results in .two products, one being a sulfur dioxide extract containing most of the toluene, asmall proportion of paraffin hydrocarbons of boiling point close to that of toluene and a substantial -proportion of paraffin hydrocarbons of higher boiling point, and the second being a rafiinate containing kerosene or other wash oil. the light parafiin hydrocarbons itcontains, the lighter fraction being returned to the feed to the system if its toluene content is sufiicientto warrant'this, and the heavier free:

1 tion beingrecycled.

Operation in accordance with the invention has importantadvantages in providing inexpensive yet quite complete recovery of toluene in highly purified form from admixture with parafiin hydrocarbons of similar boiling point. The final distillation for the separation of the toluene from kerosene or the like is easily carried out because of the wide difference in boiling points. fsimilarly, the separation of the kerosene or the like from light hydrocarbonsin the kerosene raffinate is simple because of .the relatively small proportion of light boiling hydrocarbons in this mixture. In addition; because of this'small volume of the lighthydrocarbons in this mixture, they may be recycled to the feed, for recovery of the toluene therein.

The invention will be further described in connection with the appended drawing, which illustrates in a diagrammatic manner, apparatus 7 suitable for the practice of the invention.

- fin hydrocarbons of similar boiling point issupplied somewhat below the middle of the upper section through the line [8.

The sulfur dioxide passes downwardly through the tower countercurrent' to the hydrocarbon feed, and extracts from the hydrocarbon substantially all of the toluene which it contains. The sulfur dioxide extract is removed from the bottom of the upper section through the line 20, and as removed, it containsthe sulfur dioxide, nearly all of the toluene and a substantial amount of paraflin hydrocarbons having a boilthe sulfur dioxide is removed for recycling through the storage tank 26 while the hydrocarbon bottoms are led through the line 28 for use in gasoline.

The sulfur dioxide extract removed from the bottom of the upper section through the line is supplied through the line 30 to the upper part of the lower section of the tower. lierosene or other hydrocarbon oil having a boiling point substantially higher than toluene, for example, having a boiling range of 363-490' F. is supplied to the lower portion of this section through the line 32. The kerosene and sulfur dioxide pass through the tower countercurrently and in intimate contact, with replacement of most of the light paraffin hydrocarbons in the extract by heavier pare affin hydro-carbons from the kerosene.

The kerosene raffinate is removed from the top of this section through the line 34', and intro' duced intothe sulfur dioxide still 36, wherethe sulfur, dioxide which it contains is removed and returned to the sulfur dioxide tank through the lines.36 and it. The kerosene raffinate containing light hydrocarbons is then passedthrough the line 'ii! to the splitter or still 44 in which the light hydrocarbons are removed from the kerosene. The light hydrocarbons are passed. through the line 453 and introduced with the, original feed to the upper section l2 of the column'l@,' if it contains sufficient toluene to warrant further processing for its recovery. The'kerosene fraction is recycled through the line 38 to the lower section of the column ML The kerosene washed extract is removed from the bottom of the section i l through the line 50,v

and introduced into the sulfur dioxide still .52. The sulfur dioxide removed in this still is recycled through the line Ml, while the hydrocarbon fraction containing kerosene and nearlyall of the toluene is removed through theline 5t, treated with acid in the acid treater 56 and then subjected to distillation in the still 58 to 'separate'the I claim:

1. The process of separating toluene from a mixture of toluene and paraifin hydrocarbons of similar boiling point which comprises intimately contacting said mixture with sulphur dioxide in an extracting treatment, separating the composite mixture; into two component parts consistingfof a raffinate phaseand a primary extract phase, bringing said primary extract phase Without removal of sulphur dioxide therefrom into intimate contact with a paraffin hydrocarbon having a, boiling point substantially higher than that of toluene in a washing treatment, separat- 1" i-ngithe produotsiof said washing treatment into two, component parts consisting of a washed extract component and a spent Wash oil component,

separating hydrocarbons having boiling points toluene from the kerosene and any heavier products that may have been formed. The toluene is removed from the top of the tower through the line Gil as a relatively pure product which may contain 98.5% or more toluene;

Sulfur dioxide and kerosene to replace losses may be supplied through the'lines 62 and 6.4, re-& spectively.

In operatiomfor each 10Gparts of'a' hydrocarbon fraction containing about tolue'ne, about 100 parts of sulfur dioxide and parts of kerosene may be used, with recovery of substantially all of the toluene as a 98.5% product.

If desired, to reduce the amount ,of toluene removed through the line 34, additional'sulfur dioxide may be supplied through the line 66, but this is not necessary; particularlyif the light hydrocarbon separated from theikerosene the still 44 is recycled to the feed.

.similar to'toluene from said spent wash oil component by distillation, and recovering toluene from said washed extract component by distillation.

2. The process of separating toluene from' a mixture of toluene and parafiin hydro-carbons of similar boiling point which comprises intimately contacting said mixture with sulphur dioxide in an extracting treatment, separating the composite mixture into two component parts consisting of a ramnate phase and a primary extract phase, bringing said primary extract phase without removal of sulphur dioxide therefrom into intimate contact with a paraffin hydrocarbon having a boiling point substantially higher than that of toluene, in a washing treatment, separat ing the products of said-washing treatment into two component part consisting of a Washed extract component and a spent wash oil component, separating hydrocarbons having boiling points similar to toluene from said spent wash oil component by distillation and returning the thus separated hydrocarbons to the first-mentioned extracting treatment, and recovering toluene from said washed extract component by distillation.

3. The process of separating toluene from a mixture of toluene and parafiin hydrocarbons of similar boiling .pointwhich comprises intimately contacting said mixture with sulphur dioxide in an extracting treatment, separating the composite mixture into two component parts consisting of a rafiinate phase and a primary extract phase, bringing said primary extract phase without removal of sulphur dioxide therefrom and in the absence of additional sulphur dioxide from an extraneous source into intimate contact with a paraiiin hydrocarbon having a, boiling point substantiallyhigherthan that of toluene in a washing treatment," separating the products of saidwashing treatment into two componentparts consisting of awaished extract component and aspen't wash oil component, separatin'ghydrocarbons having boiling points similarto toluene from said spent wash oil component by distillationand returning the thus separated hydrocar-f bone, to the first-mentioned extracting treatment, and recovering toluene from said washed extract component by distillation.

.. THOMAS E. KIMBALL. 

